1. Field of the Invention
The present invention relates to a ball screw, and more particularly to a chips dischargeable wiper that is disposed at the end of the nut, the wiper is simply structured for reduction of resistance, and not only can prevent intrusion of foreign objects but also can'prevent leakage of lubricating oil.
2. Description of the Prior Art
With the constant advancement of the precision feeding system, various linear transmission mechanisms, such as linear guideway, ball screw, etc, have come into existence in our everyday life, in manufacturing factories and in high-tech society. Above all, large-scale precision mechanisms are usually equipped with ball screws (either large or small), or linear guideway systems. Although the technology for linear transmission element is developing fast, consumers still expect optimum to come. Therefore, improvements have to be made. Such a desire for constant improvement of technology is quite strong in many high precision mechanism-manufacturing fields (such as wafer process equipment, CNC equipment, etc) that require more stability and less noise. For this matter, the existing linear mechanism needs a better solution.
A commonly used conventional ball screw is shown in FIG. 1, a nut 12 with a wiper 11 is disposed at either end of the nut 10, the wiper 11 is provided with a protruding edge 111 for preventing intrusion of foreign objects or loss of lubricating agent. However, in order to compensate the manufacturing error, an interval (approximately 0.25 mm) is usually reserved between the protruding edge 111 of the wiper 11 and the helical groove 101 of the screw shaft 10, plus the manufacturing error will further increase the reserved interval. According to the data well known in the art, that any foreign object whose size is larger than 0.17 mm will cause damage to the ball screw. Therefore, the reverse interval (approximately 0.25 mm) will have the problem of the intrusion of foreign objects and the loss of lubricating agent.
At this moment, in order to have a better scraping effect, a part of the protruding edge 111 as shown in FIG. 1 can be designed such that it is radially moveable, and an elastic member 112 is arranged in the protruding edge 111 for enabling the wiper 11 to press closely against the surface of the helical groove 101 of the screw shaft 10. However, the manner of pressing the surface of the wiper 11 completely against the surface of the helical groove 101 will substantially increase the friction therebetween, causing a great reduction in the mechanical efficiency of the ball screw. Furthermore, a large number of foreign objects will be likely to accumulate in the contacting area between the wiper 11 and the helical groove 101.
In view of the aforesaid reasons, the existing improvements to the linear transmission type ball screw generally involves the following two methods:
A. As shown in FIG. 2, the wiper 13 also uses its protruding edge 31 to prevent the intrusion of foreign objects and the loss of lubricating agent. In addition, a spring coil 14 is disposed behind the protruding edge 31 for increasing the radial clamping force thereof, and the protruding edge 31 are defined with a plurality of notches 132 in order to reduce friction. However, such design has a problem that, during rotation, foreign objects will rapidly accumulate in and block the notches 132 (in the feeding direction), and the foreign objects will always reside on the screw shaft. Besides, the radial clamping force 14 of the spring coil 14 will substantially increase the friction of the protruding edge 131, causing a great reduction in mechanical efficiency of the ball screw. The spring coil will also be loosened by abrasion, causing resistances and instability in foreign-objects preventing effect.
B. As shown in FIG. 3, which shows a wiper structure disclosed by U.S. Pat. No. 6,732,599, wherein the wiper 15 is disposed between the nut and a stopper, and a plurality of wiping plates 151 are annularly arranged on the wiper 15. Each of the wiping plates 151 is defined with a slant end 152 facing the helical groove of the screw shaft. By such arrangements, the slant ends 152 in the feeding direction will rotate forward and wipe off the foreign objects in the helical groove, and the slant ends 152 in the opposite direction will rotate backward without causing resistance. The aforesaid conventional product can achieve the function of wiping off the foreign objects under the condition of reducing the resistance. However, such design is too complicated and its assembly is difficult, and is unapplicable to small ball screws. Under the limitation of the cost and assembly, this design is impossible to meet the market's needs.
It is learned from the above that the conventional wiper must be cleaned, replaced or repaired periodically, otherwise, the accumulated foreign objects and grease will affect the operation of the ball screw.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.